Many public and private groups, such as security and safety personnel (e.g., police, fire fighters and ambulance drivers) use various communication networks of differing technologies and types for communication. Many networks utilize land mobile radios communicating through push-to-talk technologies. However, communications among different endpoints of different networks such as endpoints of different police, fire or other security networks may be difficult. Collaboration between the different agencies and networks tends to be ad hoc and inefficient. When achieved, it often involves laborious manual intervention. Organizations working towards interoperability solutions include Raytheon JPS Communications, IP Blue, Twisted Pair, M/A-COM and Cisco Systems.
Some interoperability solutions encounter problems, such as problems with congestion. If, for example, several different agencies were to all have users communicating with one another, such as in a large emergency situation, the communications may become lost or garbled due to congestion. Certain protocols, such as multi-level preemption protocol (MLPP), provide a means for higher priority users to preempt lower priority users. However, this often causes the interruption of lower priority users. Furthermore, if the radio lacks the ability make the user and/or device visible it is not possible to implement MLPP.